This invention relates to the field of near-field, radio frequency (RF) irradiation dosimetry, and more particularly to provision of a practical and field-usable method and apparatus for determining potentially hazardous electromagnetic radiation near radio frequency emanating devices such as transmitting antennas, RF plastic welders, and the like.
Certain standards have been set for allowable levels of RF radiation of persons and, while these may change from time-to-time as more is learned abut the effects or hazards of radiation, there exists a need for suitable means to carry out accurate and reliable measurements of the near-field specific absorption rate (SAR) of persons subjected to radiation by non-ionizing radio frequency radiation (RFR) in the frequency range from 10 KHz to 300 GHz. For example, one standard limits an allowable SAR, in watts per kilogram, for a localized point of measurement or "hot spot" to 8.0 W/kg averaged over any 1 gram of tissue, and an average SAR of 0.4 W/kg for the whole body averaged over any 6 minute period. A variety of transmitting antennas are used on board ships and are often located in or near areas that are accessible to personnel who may be subject to radiation greater than are believed safe. Moreover, especially in shipboard and other areas where a variety of conductive structures abound, unintentionally tuned or resonant conditions may exist that cause RF radiation at locations other than at the principal emitter and hence produce an unexpectedly hazardous situation.
Prior methods and means for measurement of radiation have included implantable E-field (electric field) probes and thermal probes, the latter relying on the known fact that tissue temperature rise is related to absorbed RF radiation. These devices are subject to a number of limitations that make whole body SAR assessment very difficult. These limitations include inability of prior art probes and their associated instrumentation to integrate accurately the irradiation variables over the entire body mass of a person subjected to a variety of primary and secondary radiation sources.